Method of manufacturing a wall structure and a machining tool

ABSTRACT

A method of manufacturing a wall structure includes producing at least one elongated web in a workpiece by feeding a machining tool along the workpiece, wherein the machining tool simultaneously machines a first side surface of the web, a second side surface of the web and a top surface of the web.

BACKGROUND AND SUMMARY

The present invention relates to a method for manufacturing a wallstructure. The method is particularly directed to manufacturing a wallstructure, which is capable of withstanding a high thermal load, andespecially to an engine wall structure. The method is specificallydirected to manufacturing the wall structure of a thrust chamber (acombustion chamber and/or an outlet nozzle) for use in a rocket engine.The invention is further directed to a machining tool configured forbeing used in a step in the manufacturing method.

During operation, a rocket nozzle is subjected to very high stresses,for example in the form of a very high temperature on its inside (in themagnitude of 800° K.) and a very low temperature on its outside (in themagnitude of 50° K.). As a result of this high thermal load, stringentrequirements are placed upon the choice of material, design andmanufacture of the outlet nozzle. At least there is a need for effectivecooling of the outlet nozzle.

The wall structure forming the outlet nozzle has a tubular shape with avarying diameter along a centre axis. More specifically, the outletnozzle wall structure has a conical or parabolic shape. The outletnozzle normally has a diameter ratio from the aft or large outlet end tothe forward or small inlet end in the interval from 2:1 to 4:1.

The outlet nozzle wall structure comprises cooling channels extendingbetween an upstream end and a downstream end of the nozzle. According toone previously known design, the outlet nozzle wall structure comprisesan inner wall, to which hot gas is admitted during engine operation andan outer wall, which is colder than the inner wall during engineoperation. There is a plurality of elongated webs connecting the innerwall to the outer wall dividing the space between the walls into aplurality of cooling channels.

During engine operation, any cooling medium may be used to flow throughthe cooling channels. Regarding a rocket engine, the rocket engine fuelis normally used as a cooling medium in the outlet nozzle. The rocketengine may be driven with hydrogen or a hydrocarbon, i.e. kerosene, as afuel. Thus, the fuel is introduced in a cold state into the wallstructure, delivered through the cooling channels while absorbing heatvia the inner wall and is subsequently used to generate the thrust. Heatis transferred from the hot gases to the inner wall, further on to thefuel, from the fuel to the outer wall, and, finally, from the outer wallto any medium surrounding it. Heat is also transported away by thecoolant as the coolant temperature increases by the cooling. The hotgases may comprise a flame generated by a combustion of gases and/orfuel.

According to a known method, for manufacturing the outlet nozzle, in afirst step, a first machining tool (a turning lathe) is used for workingan external surface of the workpiece in order to achieve a desiredworkpiece thickness. In a second step, a second machining tool (amilling cutter) with two spaced rotary machining elements in the form ofcutting wheels is used. The cutting wheels are arranged at a mutualdistance corresponding to a desired web thickness. The milling cutter isfed across an external surface of a cylindrical workpiece forming twogroves and an intermediate web. The cutting wheels work on the sidesurfaces of the web.

The milling cutter is indexed in the circumferential direction of theworkpiece and run, wherein a plurality of webs are produced. Thus, thewebs are integrated in and project from an inner wall. Subsequently, anouter wall is positioned around the inner wall, and joined to the edgesof the webs by welding.

It is desirable to provide a method for manufacturing a wall structureprovided with cooling channels which extend in a diverging manner, whichcreates conditions for a faster operation, and robustly achieved channelheight, than previously known methods. The invention is especiallydirected at manufacturing a tubular wall structure with an increasingdiameter with axial position and particularly suited for a rocket enginemember.

According to an aspect of the present invention, a method comprises thesteps of producing at least one elongated web in a workpiece by feedinga machining tool along the workpiece, wherein the machining toolsimultaneously machines a first side surface of the web, a second sidesurface of the web and a top surface of the web.

In this way, all three surfaces (side surfaces and top surface) of theweb are worked in one single run. The height, which is very importantfor the cooling performance, of the web is determined by the position ofan intermediate machining element in the machining tool. Thus, the firstturning step according to prior art may be dispensed with.

Further, prior art problems relating to grindings sticking between thetwo cutting wheels are decreased or prevented. All in all, a morereliable manufacturing process is achieved.

It is also desirable to provide a machining tool adapted formanufacturing a wall structure provided with cooling channels, whichcreates conditions for a faster operation than previously known methods.

According to another aspect of the present invention, a machining toolcomprises a first rotary cutting element and a second rotary cuttingelement, wherein the first and second rotary cutting elements arepositioned at a distance from each other, wherein the machining toolcomprises, a third rotary cutting element arranged between the first andsecond rotary cutting elements.

Further preferred embodiments and advantages will be apparent from thefollowing description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described in the following, in anon-limiting way with reference to the accompanying drawings in which:

FIG. 1 is a front view of a machining tool according to a firstembodiment,

FIG. 2 is a perspective view of the machining tool of FIG. 1,

FIG. 3 is a perspective view of a tubular workpiece with a varyingdiameter, which has been machined by the machining tool in a first step,

FIG. 4 shows the tubular workpiece of FIG. 3, wherein it has beenmachined by the machining tool in a plurality of steps by indexing themachining tool in the circumferential direction of the workpiece,

FIG. 5 shows the tubular workpiece after a further machining step,

FIG. 6 shows application of a cover jacket onto the machined workpiece,

FIG. 7 shows a perspective view of a wall structure resulting from themethod step of FIG. 6, wherein the wall structure defines a doublewall/sandwich structure,

FIG. 8 is a partial sectional view along the line A-A in FIG. 7, and

FIG. 9 corresponds to the view of FIG. 8 with added wall structurewelds.

DETAILED DESCRIPTION

FIGS. 1 and 2 schematically shows a machining tool 1. The machining tool1 comprises a first rotary cutting element 2 and a second rotary cuttingelement 3, wherein the first and second rotary cutting elements 2,3 arepositioned at a distance from each other. The machining tool 1 furthercomprises a third rotary cutting element 4 arranged between the firstand second rotary cutting elements. Each of the rotary cutting elements2,3,4 has the shape of a circular disc with a cutting surface in theform of cutting teeth 5,6,8 at the periphery.

More particularly, the first and second rotary cutting elements 2,3 haveparallel axes of rotation 7, and wherein the first and second rotarycutting elements 2,3 are positioned at a distance from each other in thedirection of the axes of rotation 7. More particularly, the first andsecond rotary cutting elements 2,3 form two spaced cutting wheelsarranged at a mutual distance corresponding to a desired web thickness.

The third rotary cutting element 4 is configured to machine a surfacesimultaneously with the first and second rotary cutting elements 2,3.

A cutting surface 5 of the third rotary cutting element 4 is located ata different distance from a cutting surface 6 of the first rotaryelement 2 in a direction perpendicular to the axis of rotation 7 of thefirst rotary cutting element 1. More particularly, the cutting edge 5 ofthe third cutting element 4 is located at a smaller distance from theaxis of rotation 7 than the cutting edge 6 of the first rotary element2. A cutting edge 8 of the second rotary cutting element 3 is located atsubstantially the same position in a direction perpendicular to the axisof rotation 7 as the cutting edge 6 of the first rotary cutting element2.

By feeding the machining tool 1 along a workpiece 9 while rotating therotary cutting elements 2,3,4 and bringing the rotary cutting elements2,3,4 in contact with the workpiece, two parallel grooves 10,11 and anintermediate elongated web (or rib) 12 are achieved in the workpiece 9.

The axis of rotation of the second rotary cutting element 3 is inparallel with the axis of rotation 7 of the first cutting element 2.More precisely, the axes of rotation of the first and second rotarycutting elements 2,3 are co-axial. Similarly, the axis of rotation ofthe third rotary cutting element 4 is in parallel with the axis ofrotation 7 of the first cutting element 2. More precisely, the axes ofrotation of the first, second and third rotary cutting elements 2,3,4are co-axial.

The first, second and third rotary cutting elements 2,3,4 are configuredto rotate in unison at the same speed. Further, the first, second andthird rotary cutting elements 2,3,4 are preferably arranged on a commondrive shaft 13.

The cutting edge 5 of the third cutting element 4 extends oversubstantially the complete distance between the first and second rotarycutting elements 2,3.

A first embodiment of a method for manufacturing a tubular wallstructure with varying diameter, especially configured for withstandinghigh thermal load in operation and particularly for a rocket enginecomponent in the form of an outlet nozzle, is described below withreference to FIG. 3-9.

A workpiece 9 with a cylindrical shape is used as a starting material.More specifically, the workpiece 9 is tubular with a circular crosssection, wherein a cross section diameter varies in an axial direction14 of the workpiece. Thus, the workpiece 9 forms a hollow component.More specifically, the workpiece 9 presents a rotational symmetric outersurface. The diameter of the workpiece 9 continuously increases withaxial position in one direction along the axial direction 14. Further,the workpiece 9 has a substantially uniform thickness and is preferablyformed by a sheet metal. In some cases a forging or casting, withvarying thickness along the axial direction 14 could be preferred.

The method comprises machining an external surface 15 of the workpiece 9by means of the machining tool 1. More particularly, the methodcomprises the step of producing an elongated web 12 in the envelopesurface 15 of the workpiece 9 by feeding the machining tool 1 along andinto the workpiece from a first end 16 towards a second end 17 of theworkpiece 9 in the axial direction 14. Thus, the machining tool is fedalong a curved line matching the contour of the workpiece 9. In otherwords, the method comprises milling two parallel grooves 10,11 in theouter surface of a monolithic channel wall section.

The first end 16 has a smaller cross section diameter than the secondend 17. The machining tool 1 simultaneously machines a first sidesurface 18, a second side surface 19 and a top surface 20 of the web 12,see FIG. 1.

In other words, the method comprises simultaneously machining a base(depth) of the first groove 10, which defines the first side surface 18of the web, and a base (depth) of a second groove 11, which defines thesecond side surface 19 of the web 12.

Referring now to FIG. 4, the method comprises the steps of producing aplurality of spaced elongated webs 12,112,212 in the same way byindexing said machine tool 1 a distance in a circumferential directionof the workpiece 9 after each web is produced. More particularly, themachining tool 1 is indexed such a distance in the circumferentialdirection that the first rotary cutting element 2 is positioned in thegroove 11 produced by the second rotary cutting element 3 in theprevious step. Due to the varying diameter of the workpiece 9, the webs12,112,212 are produced so that they extend in a diverging manner fromthe first end 16 to the second end 17.

A non-machined, triangular region 21,121 of the workpiece 9 is leftbetween two produced adjacent diverging webs 12,112,212. This region21,121 is machined in a later step, preferably by means of an additionalmachining tool, specifically adapted for removing such a region. Thenon-machined region 21,121 is machined in the later step to such anextent that a workpiece surface between the produced webs is, ifdesired, substantially even, see FIG. 5. More particularly, thenon-machined region 21,121 is machined in the later step to such anextent, if desired, that a workpiece thickness is substantially constantbetween the webs 12,112,212. Preferably, the workpiece 9 is machined bymeans of the machining tool 1 in consecutive, indexed runs all aroundits circumference first, and then all the non-worked regions 21,121 aremachined in later steps.

Referring now to FIG. 6, an inner wall 25 is formed withcircumferentially spaced elongated webs 12,112,212 projecting from theinner wall 25 and at right angles to the wall. Thus, the webs 12,112,212are integrated in the inner wall 25. In other words, the inner wall 25and the webs 12,112,212 are formed in one-piece. The inner wall 25 formsa cylinder and is preferably continuous in a circumferential direction.

The method comprises the step of applying a cover jacket (or second wallelement) 22 onto the workpiece 9 after said webs are formed and thenon-worked regions are removed. The cover jacket 22 has a cylindricalshape which is complementary to the shape of the workpiece 9. Thus, thecover jacket 22 is tubular with a circular cross section, wherein across section diameter varies in an axial direction 14. Moreparticularly, an internal surface of the cover jacket 22 is adapted tofit tightly onto the external surface of the webs 12,112,212. The coverjacket 22 is moved in the axial direction 14 relative to the workpiece 9until it is fitted onto the workpiece 9.

FIG. 7 shows a wall structure 23 formed when the cover jacket 22 isapplied onto the workpiece 9. The webs 12,112,212 are adapted to formmid walls between the inner wall 25 and the outer wall 22 formed by thecover jacket. Thus, the webs form distancing elements for keeping adistance between the inner and outer walls 25,22. FIG. 8 shows a crosssection A-A from FIG. 7.

Thus, the tubular outer wall 22 is positioned around the inner wall andthereafter attached to the workpiece 9, preferably via joining it to theedges of the webs 12,112,212 by welding from an outer side of the outerwall relative to the cooling channels, see FIG. 9. Thus, the wallstructure 23 forms a welded sandwich structure.

Preferably, laser-welding is used for joining the outer wall 22 to thewebs. The welding is performed in such a way that the joined-togetherportions of the wall 22 and each web 12,112,212 form a T-shaped joint26, see FIG. 9. Suitable selection of material parameters and weldingparameters makes it possible to obtain a T-shaped joint with roundedcorners, or at least a relatively smooth transition, between the walland the respective web. This results in a high-strength construction andthus an extended life. Alternatively, a construction with thinner wallthicknesses and thus reduced weight can be obtained.

In order that the welded joint comes to lie in exactly the correctposition, a previously known joint-tracking technique can be used.

Elongated channels 24 are formed between the webs 12,112 and the coverjacket 22. The elongated channels 24 are adapted for internal cooling.Thus, a cooling channel cross section area increases progressively indirection from the first end 16 (inlet end) of the wall structure 23 tothe second end 17 (outlet end).

More specifically, the wall structure 23 forms an engine wall structure.The wall structure 23 forms a rocket engine member for a thrust chamber.The thrust chamber is a combustion chamber with an outlet nozzle forexpansion of the combustion gases. More specifically, the wall structureforms an outlet nozzle for use in a liquid fuel rocket engine. Theliquid fuel is for example liquid hydrogen.

The nozzle 23 is cooled with the aid of a cooling medium that ispreferably also used as fuel in the particular rocket engine. Theinvention is however not limited to outlet nozzles of this type but canalso be used in those cases in which the cooling medium is dumped afterit has been used for cooling.

The materials used for the walls 25,22 and webs 12,112,212 consist of orcomprise weldable materials, such as stainless steel, for example of thetype 347 or A286. Use can alternatively be made of nickel-based alloyssuch as, for example, INCO600, 1NCO625, INCO718 and Hastaloy x.According to other variants, cobalt-based alloys, for example of thetype HAYNES 188 and HAYNES 230, can be used. Various types of aluminumalloys can also be used. Combinations of different materials are alsopossible.

For the welding operation, laser-welding is preferably used, but othertypes of welding arrangement, for example an electro-beam welder, canalso be used according to the invention.

By accurate matching of the welding procedure, material selection anddimensions of walls and webs, the laser-welding produces the T-shape atthe joint and also a softly rounded shape on the inner corners betweenthe outer wall 110 and the web edge. Welding is suitably effected bymeans of a continuous weld. The rounded shape of the welded jointsresults in a high-strength construction and thus a long life of thecomponent. This type of joining together affords opportunities forcomplete fusion of the welded joint and fine transitions between theparts.

In order to obtain a desired diameter ratio of the outlet nozzle, thecross sectional area of the cooling channels must increase towards thepart of the nozzle with a larger diameter. The nozzle is thereforenormally built in several sections in the axial direction. The number ofwebs is larger in the nozzle section with larger diameter. Adjacentaxial sections are joined by a weld at the inner wall. The webs areinterrupted and a manifold is arranged in a tangential direction betweenthe ends of the webs forming a tangential cooling duct.

The invention is not limited to the above-described embodiments, butseveral modifications are possible within the scope of the followingclaims.

According to an alternative to laser welding, soldering may be used toattach the outer wall to the webs. Further, solid state welding, e.g.friction welding may be used. According to a further alternative, theouter wall is built up via an electrochemical process, such as plating.

According to an alternative embodiment, the wall structure is configuredto form an aircraft engine component, such as turbine engine housing.

Further, the invention is not limited to being applied to circularcylindrical structures, but may as well be applied on a substantiallyflat sheet. The sheet may in a later stage be curved to form saidcylindrical shape.

1. A method of manufacturing a wall structure for a rocket engine nozzlecomprising the steps of providing a workpiece with a cylindrical shapehaving a circular cross section which cross section diameter varies inan axial direction of the workpiece, producing a plurality of spacedelongated webs in the workpiece by feeding a machining tool along theworkpiece, wherein said plurality of spaced elongated webs are producedby indexing said machine tool in relation to the workpiece, wherein thewebs are produced so that they extend in a diverging mariller from afirst end of the work piece to a second end of the work piece and whichwebs are distributed around the circumference of the workpiece, whereinin a step of producing one elongated web the machining toolsimultaneously machines a first side surface of the web, a second sidesurface of the web and a top surface (20) of the web.
 2. A methodaccording to claim 1, comprising the steps of simultaneously machining abase of a first groove, which defines the first side surface of the web,and a base of a second groove, which defines the second side surface ofthe web.
 3. A method according to claim 1, wherein a nonmachined regionof the workpiece between two produced adjacent diverging webs ismachined in a later step.
 4. A method according to claim 3, wherein thenonmachined region is machined in the later step to such an extent thata workpiece surface between the produced webs is substantially even. 5.A method according to claim 4, wherein the non-machined region ismachined in the later step to such an extent that a workpiece thicknessis substantially constant between the webs.
 6. A method according toclaim 1, comprising the step of applying a cover jacket onto theworkpiece after said webs are formed and attaching the cover jacket tothe workpiece, wherein elongated channels are formed between the websand the cover jacket.
 7. A method according to claim 1, wherein theworkpiece has a cylindrical shape and comprising the steps of producingsaid web on an external surface of the cylindrical workpiece.
 8. Amethod according to claim 1, comprising the step of applying an annularcover jacket around the cylindrical workpiece after said webs are formedin the external surface of the workpiece.
 9. A method according to claim1, comprising the step of configuring the wall structure to withstand ahigh thermal load in operation.
 10. A method according to claim 3,wherein the non-machined region is machined in the later step to such anextent that a workpiece thickness is substantially constant between thewebs.